Advanced guard rail

ABSTRACT

An advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising:
         a frame; and   a hook provided at each respective corner of the frame, each hook configured to receive a rung of a respective end frame therein, wherein the distances between the upper hook centres and the lower hook centres are dissimilar, to add additional stiffness to the access tower in use.

FILED OF THE INVENTION

The present invention relates to an advanced guard rail connectable between two respective end frames. The present invention further relates to an access tower comprising an advanced guard rail.

BACKGROUND OF THE INVENTION

Access towers are known and provide a quick and efficient way of erecting (and subsequently dismantling) a scaffolding structure. Whereas traditional scaffolding structures are constructed from a plurality of discrete scaffolding poles and connectors, access tower systems provide a number of interchangable modular components, configured to fit together to create an access tower of a desired height.

A known access tower comprises two ‘ladder-like’ end frames, connected by a number of structural bracing elements. Platforms (decks) are provided between the end frames to provide work surfaces. The provision of the bracing elements adjacent to a platform, together with the rungs of the end frames above the platform level, effectively provide a guard rail arrangement around the platform, improving safety. However, when additional levels of the access tower are being constructed, the bracing elements may not yet be securely in place, increasing the risk of the installer falling from the tower.

To address the issue, it is known to use an advanced guard rail, which provides a temporary guard rail adjacent the subsequent level to be constructed. The advanced guard rail is positioned in place while standing on a completed level. Once the bracing elements of the subsequent level are in place, the advanced guard rail may be removed and re-used for the construction of the next level.

However, the use of an advanced guard rail adds an additional component and installation step to the access tower system. It has become desirable to use an advanced guard as a structural, as well as safety, component, such that an advanced guard rail may be used as a substitute for the bracing elements.

Any scaffolding structure must be stable, to withstand a certain amount of lateral loading and to be suitable for use as a safe work platform. In addition, it is desirable that a scaffolding structure provides a certain amount of rigidity (stiffness), to allow the user to work effectively. For example, undesirable play in the scaffolding structure in use might prevent a user from carrying out precision painting tasks.

This play leads to a lack of rigidity in the tower as a whole and can cause a user to infer a perceived lack of safety of the tower. A perceived lack of safety can, itself, increase the likelihood of injuries owing to the user being more tense.

In the case of traditional purpose-built scaffolding structures, an adequate number of discrete scaffolding elements and connectors are added until the desired level of rigidity has been accomplished.

However, in the case of access towers, the user is constrained to use the modular components supplied. To ensure a rigid structure, the modular components must be designed so as to positively connect with one another. However, at the same time, the connections must be such that the towers may be easily erected and disassembled. Accordingly, there is a certain amount of play afforded at connection points.

While such play can be mitigated by bracing elements, there is a desire to provide an access tower system wherein the advanced guard rail itself provides for structural rigidity of the tower.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides an advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising:

-   -   a frame; and     -   a hook provided at each respective corner of the frame, each         hook configured to receive a rung of a respective end frame         therein, wherein the distances between the upper hook centres         and the lower hook centres are dissimilar, to add additional         stiffness to the access tower in use.

Further, the present invention provides an advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising:

-   -   a frame; and     -   a hook provided at each respective corner of the frame, each         hook configured to receive a rung of a respective end frame         therein, wherein the two lower hooks further comprise a locking         mechanism, the advanced guard rail being configured such that as         the locking mechanism is closed, the advanced guard rail is         secured to the end frames by the inner surface of the upper         hooks applying a force on an upper surface of the frame and a         part of the locking mechanism applying a force on a lower         surface of the frame

Still further, the present invention provides an advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising:

-   -   a frame; and     -   a hook provided at each respective corner of the frame, each         hook configured to receive a rung of a respective end frame         therein, wherein the distance between the centre of the upper         hooks and the centre of the lower hooks is intentionally less         than the distance between the centre of the rungs with which the         hooks engage in use.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

FIG. 1 shows an access tower incorporating an advanced guard rail embodying the present invention;

FIG. 2 shows a side view of an advanced guard rail embodying the present invention;

FIG. 3 shows a hook and locking mechanism of an advanced guard rail embodying the present invention;

FIG. 4 shows a partial cut-away view of the hook and locking mechanism of FIG. 3; and

FIGS. 5 and 6 schematically illustrate the forces imposed by the advanced guard rail embodying the present invention;

DETAILED DESCRIPTION OF INVENTION

FIG. 1 illustrates an access tower 1 in accordance with the present invention. The access tower 1 comprises two end frames 2. Each end frame 2 is comprised of a number of end frame sections 3, which are interconnectable so as to define an end frame 2 of a desired height. Each end frame section 3 comprises a pair of vertical stiles 4, inter-connected by a plurality of horizontal rungs 5. The stiles 4 of one end frame section 3 are connectable to the respective stiles of another end frame section 3 by way of a spigot and socket connection 6.

The rungs 5 of an end frame section 3 are spaced at regular intervals (“pitch”). In a known end frame section manufactured by Youngman Group Ltd, the rungs 5 have a pitch of 500 mm. Each end frame section 3 is configured such that, when two end frame sections 3 are connected to one another, the spacing between the top rung 5 of the lower end frame section 3 and the bottom rung 5 of upper end frame section 3 is the same as the pitch of the end frame sections 3 themselves. As a consequence, the rungs 5 of an end frame 2 collectively have a substantially identical pitch.

As shown in FIG. 1, each end frame section 3 of at least one end frame 2 comprises an integral ladder section 7. A wheel 8 is connected to the bottom of each stile 4 of the lower end frame section 3. Although the end frames 2 of the access tower 1 shown in FIG. 1 both comprise two end frame sections 3 of the same height, this is not essential. For example, one end frame section 3 could be shorter than another, to enable a user to configure a tower of a desired height.

The two end frames 2 are connected to one another by a plurality of horizontal 9 and diagonal 10 braces, which connect to either the stiles 4 or rungs 5 of the end frames 2.

As is further shown in FIG. 1, a work platform (deck) 11 is provided between the end frames 2, engaged with the horizontal rungs 5. The work platform 11 may comprise a hatch, as is known in the art.

The access tower 1 further includes an advanced guard rail 12 embodying the present invention (two are shown, one of which is shaded for clarity).

With reference to FIG. 2, the advanced guard rail 12 comprises an upper horizontal member 13, a lower horizontal member 14 and an intermediate horizontal member 15. Further, the advanced guard rail 12 comprises two outer vertical members 16 and two inner vertical members 17.

The outer vertical members 16 connect the upper 13, lower 14 and intermediate 15 horizontal members to one another, in a spaced apart relationship. The intermediate horizontal member 15 is arranged closer to the upper horizontal member 13 than the lower horizontal member 14. The outer vertical members 16 are connected to the upper 13, lower 14 and intermediate 15 horizontal members at a point inwards from the distal ends thereof.

In the embodiment shown, the diameter of the intermediate horizontal member 15 is larger than the diameter of the outer vertical member 16. In one embodiment, two apertures are provided at a location inwards from each end of the horizontal member 15, to receive the respective outer vertical members 16 therethrough.

The inner vertical members 17 are interconnected between the lower horizontal member 14 and intermediate horizontal member 15. The inner vertical members 17 are spaced closer to the outer vertical member 16 than to each other.

The upper 13, lower 14 and intermediate horizontal 15 members; and the outer 16 and inner 17 vertical members together define a frame of the advanced guard rail. Any connections between the members are made substantially at right angles.

A hook 18 is provided at each respective corner of the frame, and is configured to receive a rung 5 of a respective end frame 2 therein (See FIG. 1). Each hook 18 comprises a claw 25 having a substantially cylindrical inner surface. Preferably, the radius of the cylindrical inner surface is sized so as to be slightly greater than the radius of the rung 5 receivable therein. Consequently, the claw 25 may receive the rung 5 with a positive, but not tight, fit, allowing a limited amount of play. The amount of play afforded is configured to account for the combined manufacturing tolerances of the claw 25 and the rung 5.

The hooks 18 provided at either end of the upper horizontal member 13 are collectively referred to herein as the “upper hooks” (owing to their configuration in use), and are labelled as 18A and 18B in FIG. 2. Likewise, the hooks 18 provided at either end of the lower horizontal member 14 are referred to as the “lower hooks” and are labelled 18C and 18D respectively. Hook 18A is substantially identical to hook 18B; and, likewise, hook 18C is substantially identical to hook 18D, save for the fact that they extend from opposite ends of the horizontal members.

The distances between the centres of the upper hooks 18A, 18B and the lower hooks 18C, 18D are dissimilar. In other words, the distance “AB” between the centre of upper hook 18A and the centre of upper hook 18B is dissimilar to the distance “CD” between the respective centres of lower hook 18C and lower hook 18D. Preferably, the distance CD is larger than the distance AB. In one embodiment, the distance AB is substantially the same as the nominal spacing of the end frames 2 afforded by the bracing elements 9, 10. In another embodiment, the distance AB may be greater than the distance CD. In any event, the intentionally dissimilar hook centres conveniently provides additional stiffness to the access tower, as described below.

Each of the lower hooks 18C and 18D are additionally provided with a locking mechanism 20, as shown in more detail in FIGS. 3 and 4. In one embodiment, the locking mechanism comprises a lever 21 and a locking clamp 22. The locking clamp 22 is pivoted with respect to the hook assembly 18 about a pivot 34. The lever 21 is interconnected with the locking clamp 22 by a connecting rod 23 (see FIG. 4). The lever 21 is pivotable with respect to the connecting rod 23. There is a floating connection between the connecting rod 23 and the locking clamp 22. Specifically, the end of the connecting rod 23 includes a pin 28 which rides in a respective groove 29 provided in the locking clamp 22. The pin 28 and groove 29 are configured to increase the extent of pivoting of the locking clamp 22.

A compression spring 24 urges the locking clamp 22 away from the claw 25 of the hook 18.

The lever 21 has a cam surface 26 which engages with the surface of a washer spring 27. The profile of the cam surface 26 and compression spring 24 are configured so as to provide an over-centre locking arrangement. This is by virtue of the varying distances between the pivot point 35 and the cam surface 26. Accordingly, the lever 21 tends to ‘snap’ to either extreme of its pivotal movement with respect to the connecting arm 23. In FIGS. 3 and 4, the mechanism is shown in its locked position. The profile of the cam surface 26 co-operates with force of the spring 24 to maintain the locking mechanism 20 in its closed position. In the open position, the lever 21 rests over the claw 25 and is retained in place by virtue of the cam surface 26 and the force of the spring 24, requiring a manual force to move the lever 21 away from the open position. Such a feature aids assembly.

Further, a spring washer 27 is provided between the cam surface 26 of the lever 21 and the body of the hook 18. The spring washer 27 biases the cam surface 26 away from the body of the hook 18. Accordingly, the biasing direction of the spring washer 27 is opposite to that of the spring 24. A number of discrete spring washers 27 may be stacked together, defining a collective spring washer having a predetermined biasing force.

When a rung 5 of an end frame 2 is received (not shown) in the claw 25 of the hook 18, the locking mechanism 20 is subsequently closed by the user rotating the lever 21 to the position shown in FIGS. 3 and 4. As the lever 21 rotates towards the closed position, a contact surface 30 of the locking clamp 22 engages with a portion of the underside of the rung 5.

An advanced guard rail 12 embodying the present invention is intentionally configured such that the contact surface 30 of the locking clamp 22 will engage the underside of the rung before the lever 21 has fully pivoted to reach its closed position (shown in FIGS. 3 and 4).

As the user continues to apply a manual force on the lever 21 towards the closed position, the contact surface 30 imposes a force on the underside of the rung 5. The resultant reactionary force imposed by the rung 5 is relayed through the mechanism causing the spring washer 27 to deform against its biasing force. As a result of the deformation of the spring washer 27, the lever 21 is caused to fully rotate into its closed position and the spring washer 27 continues to impart a force on the underside of the rung 5. The cam surface 26 and the spring 24 act to maintain the lever 21 in the closed position. By virtue of the spring washer 27, any play between the rung 5 and claw 25 has thus been reduced or removed, since the contact surface 30 maintains a constant force on the rung 5.

Preferably, the distance between the upper hooks 18A, 18B and the lower hooks 18C, 18D is intentionally less than the nearest pitch of the rung spacing. When an advanced guard rail 12 embodying the present invention is mounted between two end frames 2, the claws 25 of the upper hooks 18A, 18B each receive a rung 5 of a respective end frame 2, with an inner surface of the upper claws resting on an upper surface of the rungs 5. As a result of the advanced guard rail 12 hanging from the upper hooks, the lower hooks 18C, 18D are caused to be positioned adjacent a lower set of rungs 5. However, the inner surface of the claw 25 of the lower hooks 18 does not contact the upper surface of the rung 5 but there is instead an intentional gap therebetween. This intentional gap is taken up or reduced by the resiliency provided by spring washer 27.

Thus, the distance between the centre of the upper hooks 18A, 18B and the lower hooks 18C, 18D is intentionally less than the distance between the centres of the rungs 5 with which the hooks engage.

The provision of the dissimilar centres and the locking mechanisms on the lower hook individually and collectively provide an advanced guard rail which increases stiffness in the access tower.

FIG. 5 shows the hooks 18 of an advanced guard rail embodying the present invention and further illustrates the direction of forces imposed by the hooks 18 on the rungs 5 as a result of the dissimilar hook centres (i.e. AB≠CD), in use. In the illustration in FIG. 5, distance CD is larger than distance AB.

With reference to FIG. 1, it will be appreciated that before the advanced guard rails 12 and platform 11 are put in place, the two upper end frame sections 3 are held in place by virtue of their location on the spigots provided on the lower end frame sections 3. It may be assumed that the lower end frame sections 3 are substantially vertical and therefore parallel to one another, by virtue of the bracing elements 9, 10, and platform 11 The end frame sections are thus spaced apart by a nominal predetermined distance. The spigot connection provides a certain amount of play.

When an advanced guard rail 12 embodying the present invention (having dissimilar hook centres) is located between the upper end frame sections 3, the lower hooks 18C, 18D tend to push the rungs 5 of the end frames away from one another, while the upper hooks 18A, 18B tend to hold the rungs 5 at the nominal distance apart. The advanced guard rail 12 therefore tends to force the end frames sections 3 into a trapezoidal configuration. In so doing, the bottoms of the end frame sections 3 are urged away from one another, which force acts to take up much if not all of any play in the spigot connection at the bottom of the end frame section 3, increasing the rigidity in the access tower 1 as a whole.

As more end frame sections 3 are mounted on the access tower 1, and more advanced guard rails 12 added, the trapezoidal configuration of each advanced guard rail 12 tends to cause the upper hooks 18A, 18B to push the rungs 5 of the end frame sections 3 towards one another, as shown in FIG. 5. It will be appreciated that a plurality of advanced guard rails 12 on a tower 1 alternately ‘push’ and ‘pull’ the 5 rungs of the end frame sections 3.

FIG. 6 illustrates the general direction of forces imposed by the hooks 18 by virtue of the locking mechanism 20. As described above, when the locking mechanism 20 is closed, the inner surface of the claws 25 of the upper hooks 18A, 18B applies a force on the upper surface of the upper rungs 5. At the same time, the locking clamp 22 applies a force on the lower surface of the lower rungs 5, thereby positively engaging the advanced guard rail 12 with the rungs 5 of the tower 1.

The rigid frame of the advanced guard rail 12, together with the positive engagement with the rungs 5, provides an effective triangular bracing which therefore replaces the need for discrete horizontal and diagonal bracing elements other than at the base of the access tower. Indeed, even the bracing elements 9, 10 shown in FIG. 1 may be replaced by an advanced guard rail 12 embodying the present invention, though the use of such bracing element aids the initial assembly of the lower end frame sections.

The force pairs in FIGS. 5 and 6 have been illustrated separately for clarity. They do in fact act act at the same time. In a combined illustration, the collective forces imparted by each hook would be shown to be diagonal—i.e. providing a triangular bracing arrangement.

An advanced guard rail 12 embodying the present invention conveniently reduces or avoids play in any connection points in the access tower, thereby increasing the rigidity (stiffness) of the access tower 1 and, advantageously, the perceived safety of the tower 1 to the user.

When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. 

We claim:
 1. An advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising: a frame; and a hook provided at each respective corner of the frame, each hook configured to receive a rung of a respective end frame therein, wherein the distances between the upper hook centres and the lower hook centres are dissimilar, to add additional stiffness to the access tower in use.
 2. An advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising: a frame; and a hook provided at each respective corner of the frame, each hook configured to receive a rung of a respective end frame therein, wherein the two lower hooks further comprise a locking mechanism, the advanced guard rail being configured such that as the locking mechanism is closed, the advanced guard rail is secured to the end frames by the inner surface of the upper hooks applying a force on an upper surface of the frame and a part of the locking mechanism applying a force on a lower surface of the frame
 3. An advanced guard rail according to claim 2, wherein the locking mechanism is an over centre lock comprising a lever and a clamping arm, the clamping arm applying a force on a lower surface of the frame when the locking mechanism is closed.
 4. An advanced guard rail according to claim 2, wherein the lever comprises a cam surface in contact with a part of the hook, configured such that as the lever is rotated, the locking mechanism is caused to close.
 5. An advanced guard rail according to claim 2, further comprising a spring washer between a lower hook and lever to provide the mechanism with compliance to lock against an end frame over a variable position.
 6. An advanced guard rail according to claim 2, wherein the distances between the upper hook centres and the lower hook centres are dissimilar, to add additional stiffness to the access tower in use.
 7. An advanced guard rail connectable between two respective end frames to create an access tower, the advanced guard rail comprising: a frame; and a hook provided at each respective corner of the frame, each hook configured to receive a rung of a respective end frame therein, wherein the distance between the centre of the upper hooks and the centre of the lower hooks is intentionally less than the distance between the centre of the rungs with which the hooks engage in use.
 8. An access tower comprising at least one advanced guard rail according to claim 1; and two end frames, each comprising a pair of stiles connected by a plurality of rungs spaced apart from one another, wherein the advanced guard rail is connected between the two end frames.
 9. An access tower comprising at least one advanced guard rail according to claim 2; and two end frames, each comprising a pair of stiles connected by a plurality of rungs spaced apart from one another, wherein the advanced guard rail is connected between the two end frames.
 10. An access tower comprising at least one advanced guard rail according to claim 7; and two end frames, each comprising a pair of stiles connected by a plurality of rungs spaced apart from one another, wherein the advanced guard rail is connected between the two end frames. 